Transcript EEE 490 Final Presentation

Hybrid Molecular MOS
Transistor
EEE 490 Final Presentation
EEE 490 Fall 2000, Dr. Thornton
Project Overview
• The objective of this project was to modify a Silicon on
Insulator (SOI) device to be sensitive to an environmental
condition (light).
• The molecule that is used has to be sensitive to the desired
environmental condition.
• When light hits the molecular layer, the molecule’s bonds
are broken, and forms dipoles and creates additional charge
on the silicon surface.
EEE 490 Fall 2000, Dr. Thornton
Project Overview
• The threshold voltage is measured before the device comes
in contact with light, and then after light hits the molecule
on the device.
• The threshold voltage is different due to the change in
surface potential generated by the effect of the light hitting
the molecule.
Id
V T 2 VT 1
EEE 490 Fall 2000, Dr. Thornton
Vs
Silicon on Insulator Devices
• Silicon on Insulator (SOI) is a new technology that has a
number of advantages over ordinary silicon technologies
including:
– SOI Devices are 25%-30% faster1.
– SOI Devices have less leakage current through the substrate due to the
buried insulator layer2.
– SOI Devices have reduced parasictic capacitance2.
Source:
1. Why Silicon-on-Insulator, www.semiconductor.net/semiconductor/issues/issues/2000/200008/six0008io.asp
2. SOI technology, www.iee.et.tu-dresden.de/~graupner/off/soi0_e.html
EEE 490 Fall 2000, Dr. Thornton
SOI Fabrication
(Basic Steps)
1.
2.
3.
4.
5.
Bare silicon wafer (for our case p-type).
High energy implant of oxygen atoms.
Source and Drain Boron implant.
Source, Drain, and Substrate contacts.
Addition of the molecular layer.
Drain
Source
Silicon
Silicon Dioxide
900Å
4000Å
Silicon
EEE 490 Fall 2000, Dr. Thornton
Substrate
(Gate)
Model of the Process
EEE 490 Fall 2000, Dr. Thornton
Model of the Process
EEE 490 Fall 2000, Dr. Thornton
Model of the Performance
Log Scale
Linear Scale
EEE 490 Fall 2000, Dr. Thornton
Model of Molecular Layer
• To model the shift in threshold voltage we attempted it by
two different methods:
– applied a voltage at the gate region
– put a fixed charge at the Silicon Dioxide/Silicon interface.
Gate Voltage = 0.4V
2E11 C of charge added
EEE 490 Fall 2000, Dr. Thornton
Circuit
• We built an external circuit to measure the threshold
voltage of the Transistor.
– We used a modified Wilson Current Mirror.
EEE 490 Fall 2000, Dr. Thornton
Circuit Output
Drain Current
600
500
Id
400
300
I(d)
200
100
0
0
0.2
0.4
0.6
Gate Voltage
EEE 490 Fall 2000, Dr. Thornton
0.8
1
IV Characteristics
Vd=10mV
Linear Scale
Log Scale
Drain Current
1.20E-07
1.00E-05
Vt1=9.6V
Vt2=5.6V
1.00E-07
1.00E-06 0
8.00E-08
10
20
1.00E-07
6.00E-08
1.00E-08
4.00E-08
1.00E-09
2.00E-08
1.00E-10
0.00E+00
0
5
10
15
20
1.00E-11
Substrate Voltage
EEE 490 Fall 2000, Dr. Thornton
Vt1=9.6V
Vt2=5.6V
before light
contact
after light
contact
IV Characteristics
Vd=100mV
Linear Scale
Log Scale
1.20E-06
1.00E-04
1.00E-06
1.00E-05
Drain Current
0
Vt=5.4
Vt=1.9
8.00E-07
1.00E-06
6.00E-07
5
Vt=5.4
Vt=1.9
1.00E-07
4.00E-07
1.00E-08
2.00E-07
1.00E-09
0.00E+00
0
5
10
15
20
1.00E-10
Substrate Voltage
EEE 490 Fall 2000, Dr. Thornton
10
15
20
before light
contact
after light
contact
IV Characteristics
Vd=1V
Log Scale
Linear Scale
Drain Current
1.00E-05
1.00E-04
0
Vt1=4.9V
Vt2=2.2V
8.00E-06
20
1.00E-05
6.00E-06
1.00E-06
4.00E-06
1.00E-07
2.00E-06
1.00E-08
0.00E+00
1.00E-09
0
10
10
20
Substrate Voltage
EEE 490 Fall 2000, Dr. Thornton
before light
contact
Vt1=4.9V
Vt2=2.2V
after light
contact
Molecule
• We used a an alkane, that is not light sensitive and an
spiropyran, which will be responsible for creating a charge
separated stable state when irradiated with light of the
correct wavelength.
– The alkane is a 16 carbon chain with a carboxylic acid at the end.
– The spiropyran is a bicyclic system with a small chain with a carboxylic
acid on one of the rings.
EEE 490 Fall 2000, Dr. Thornton
Significance
• We were able to change the operational parameters
of a MOS Transistor by using a light sensitive
molecule.
• We were able to model the device and the device
shift using commercial software.
• This may lead to more research being performed
at ASU on a wide range of biosensors.
EEE 490 Fall 2000, Dr. Thornton
Future Work
• Duplicate Results
• Fully characterize the light sensitive transistors.
• Find applications for this device, and devices with similar
processing.
• Research other molecules, and apply them in much the
same way.
EEE 490 Fall 2000, Dr. Thornton